Castello di Monte San Giovanni Campano, Medieval castle in Monte San Giovanni Campano, Italy.

The Castello di Monte San Giovanni Campano is a medieval fortress of which two towers and parts of the palace remain. The square tower, about 20 m high, has walls 3.30 m thick at the base and a doorway set nearly halfway up; the pentagonal tower is an unusual shape for castles of this kind. The palace walls are over 2 m thick at the base, and the walls retain two bartizans and double-width patrol walks.

The castle was built at the end of the 10th century and passed to the counts of Aquino on 8 April 1157; a 1184 earthquake damaged it badly. In February 1495 Charles VIII's troops, marching on Naples, breached it with artillery placed on the hill opposite after eight hours of bombardment, then sacked the town. It returned to the Papal States in 1595 as the governor's seat, and earthquakes in 1703 and 1915 led to the demolition of its upper floors.

The castle is known for the imprisonment of Thomas Aquinas by his family from 1244 to 1245, meant to turn him from the Dominicans toward a Benedictine career as abbot of Montecassino. Tradition holds that a woman was sent to his cell and he drove her out with a burning brand. His cell became a 16th-century chapel with a blue-and-white majolica chequered floor and a Neapolitan-school triptych on panel showing scenes of his life.

The castle sits in the hills of the Lazio region, roughly 90 kilometers southeast of Rome. Access is by way of paved paths and narrow trails, so sturdy footwear and time to explore are advisable.

The pentagonal tower is unusual among castles of this type, and the two surviving towers are nearly unmodified examples of 11th-century defensive architecture. The walls also hold two bartizans, projecting corner turrets that let defenders watch the base of the walls.